1. Field of the Invention
This invention pertains to sorting machines used to sort fungible products, such as nuts and many other agricultural products, by passing the products along a channel having a viewing window and detecting products that are substandard in shade from those that are within standard limits and rejecting those that are substandard.
2. Description of the Prior Art
A typical sorter of fungible products of the type just described is comprised of one or more channels that are gravity fed from a top loaded hopper, the products flowing in the channel in a fairly constant stream and sometimes overlapping one another. The channel background is electro-optically observed through a viewing window while no products are flowing by at least one photodetector to produce an output that is representative of that background. Although only one photodetector is used in a very simple machine, it is common to employ multiple photodetectors, for example, three, viewing the product flow from various different viewing angles. The background for each photodetector is separately determined for such machines. This process of determining a signal representative of the background without product flow is know as "normalizing".
When the product flow is initiated and the actua product flow is electro-optically sensed, the background signal is subtracted from the total output so that the background is discounted in determining whether the product flow includes all standard or acceptable products or includes a substandard product now and again. Assuming the latter, when a substandard product is sensed by an electro-optical photodetector by having at least a portion of its surface area being either lighter or darker than a standard shade, then a reject signal is produced, following a suitable delay, to activate a reject mechanism, which diverts the substandard product from the channel. The delay is necessary for the product to fall below the viewing window and be opposite the reject mechanism. The reject mechanism is typically a burst or jet of air that blows the substandard product out of the ordinary channel flow to drop into a reject bin.
From time to time, product flow must be suspended for the viewing window to be either blown clean or wiped clean of dust and to again determine a new "normalizing" value for the background shade.
Although such prior art sorting machines as generally described above have used digital logic in switching from sort mode to normalizing mode and for determining the timing delay for the proper operation of the reject mechanism to expel a substandard product, the analog value of the observed shade of the product flow as a whole in the viewing window has determined the activation of the reject mechanism. In many cases, however, discrimination of substandard products in various ways is not possible with such prior art sorting machines.
For example, it is known that the background of the entire viewing window is not of uniform shade. Should a marginally shaded product be on one side of the channel as it passes the viewing window, it might pass as acceptable, whereas should the same product be on the opposite side of the channel as it passes the viewing window, it might be rejected. This is because the overall light intensity for the two passes would be slightly different. When the "normalized" value for the background is respectively subtracted, then the results would be different from each other.
Another example is the desire on occasion to pass products with small surface substandard spots, but not with larger spots. For example, almonds used in candy bars are acceptable if their skins are only slightly scraped to leave a small spot. A large scrape leaving a large spot will result in that almond being classified as substandard for many purposes. A spot of white nut meat without skin is very white when compared to the dark brown skin of an almond. When the overall light intensity of an entire viewing window determines if an almond should be accepted or rejected, it is exceedingly hard to control the setting to discriminate on the basis of spot size. This is especially true when more than one almond may be in the viewing window at the same time, each with a small spot.
Another problem that has occurred in the prior art is the "missing" of a properly detected defective product by the expelling mechanism. That is, not only must a substandard product be accurately detected, the signal for activating the reject air blast must be delayed or timed so as to expel the substandard product from the product flow. Assuming that there is a detected substandard spot that would cause a product to be rejected and that spot is on the front end, many prior art machines might cause the reject air blast to miss the product by timing the activation pulse from the spot detection. Were the spot in the middle, the timing would properly time the reject mechanism. Spot detection at the rear of a product has also, in some cases in the prior art, resulted in timing misses.
Yet another example of products virtually impossible to sort by the prior art machines are products that are abnormally short or long. That is, in many cases, broken pieces are desirably discriminated against as being substandard by being abnormally short. Abnormally long pieces are sometimes also substandard for a particular purpose. Again, abnormally long almonds are not desirable for use in a candy bar.
When products are viewed singly by the prior art machines, they can be discriminated against since they would occupy an acceptable percentage of the overall viewing window or, alternatively, as being substandard by occupying an abnormally small or large percentage of the overall viewing window. However, when the product flow is fast, as it desirably is with the newer machines, mistakes on this basis of discrimination do occur because of product overlap. A broken piece may get by when included in the viewing window with at least part of another product. Perfectly acceptable products may be rejected when they appear together by being mistaken for an abnormally long product.
Therefore, it is a feature of the present invention to provide improved observing of the viewing window of a sorting machine for shades of gray by individually observing a plurality of photo sites therein and determining substandard rejection criteria based on a logic relationship of a plurality of photo site observations.
It is another feature of the present invention to provide improved observing of the viewing window of a sorting machine by photo site locations and normalizing each photo site for background shade and the sensitivities of the photodetectors observing the respective photo sites.
It is still another feature of the present invention to provide improved observing of the viewing window of a sorting machine by photo site locations and determining when a predetermined sequential number of such photo sites exist so that spot size discrimination sorting can be achieved.
It is yet another feature of the present invention to provide improved timing of the reject mechanism in a sorting machine by applying digital timing techniques to always activate the reject mechanism from the detection of the trailing edge of the product to be rejected and to cause such rejection even when the trailing edge might be actually nondetectable because of product overlap in the viewing window.
It is still another feature of the present invention to provide improved observing of the viewing window of a sorting machine by photo site locations and by leading and trailing edge detection and logic means to discriminate against both substandard short products and long products with respect to standard length products.